1. Field of the Invention:
The present invention relates to organopolysiloxane compositions comprising polyacyloxysilanes and encapsulated hardening accelerators, and to means for the curing or hardening of such compositions into elastomers.
2. Description of the Prior Art:
The organopolysiloxane/polyacyloxysilane compositions, in contrast to the known one-component compositions which also comprise acyloxy radicals bonded to silicon atoms (described in particular in French Pat. Nos. 1,198,749, 1,220,348, 2,429,811 and published French Patent Application No. 82/13,505, filed July 30, 1982), are not storage stable, but their cross-linking time is much shorter, for example, on the order of a few minutes up to 60 minutes. They must, therefore, be prepared as and when required.
The rapidly cross-linking compositions of the above type, in which the cross-linking is independent of the degree of humidity of the surrounding atmosphere, are used in fields of application where this property is especially useful, such as, for example, the manufacture of seals "in situ" in the automobile industry. Compositions of the above type, comprising acyloxy radicals bonded to silicon atoms and having a cross-linking time independent of the humidity of the ambient air, are described, for example, in British Patent Specification No. 1,308,985, which features a hardening process which consists of adding to the subject compositions from 3 to 15% of a hardening accelerator comprising a silico-aluminate which has from 5 to 10% by weight of adsorbed water, with a view towards manufacturing silicone elastomer moldings by low pressure injection.
In published French Patent Applications Nos. 83/01,504 and 83/01,505, filed Jan. 27, 1983, compositions are described which are also of the foregoing type, but in which the hardening accelerator is selected, respectively, from among an alkali metal hydroxide and alkaline earth metal hydroxide, or is alternatively a mixture consisting of water and a phosphate and/or a polyphosphate of an alkali metal or of an alkaline earth metal.
The accelerators described in the immediately aforesaid two French patent applications have enabled very significant progress to be made, relative to the teachings of British Pat. No. 1,308,985, in the sense that, on the one hand, the nature and quantities of accelerators introduced do not modify the mechanical properties of the resultant elastomer and, on the other hand, these accelerators have offered the possibility of using compositions of such type for glueing or mating parts which are circulating on industrial assembly lines where there are no storage areas available for them in which their complete hardening could be assured.
However, the compositions described in the '985 British patent and the two published French patent applications cannot be singly packaged (one-component compositions) and must be packaged as two components, typically the organopolysiloxane as one component and the accelerator on the other, since the mixing of these two components must be done as and when required, namely, at the point in time of use.
This procedure is fraught with disadvantages. First, there is naturally the risk that at the time of use the respective proportions of the two components are not measured out correctly. Furthermore, especially in the case of the automatic manufacturing of "formed" or "in situ" seals, the mixing is carried out in an automatic apparatus for depositing the compositions, and comprising a mixing head which receives the polysiloxane composition and the accelerator. It is then necessary that the compositions used in this apparatus have a well regulated hardening time to avoid the mixture solidifying in the mixing head, and this requires long and critical optimization trials. Furthermore, it is necessary to empty these mixing heads when the apparatus is stopped or has broken down, to avoid solidification occurring.